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Statement I: Thin films such as soap bub...

Statement I: Thin films such as soap bubble or a thin layer of oit on watar show beautiful colors when illuminated by white light.
Statement II: It happens due to the interference of light reflected form the upper surface of thin film.

A

(a) If both assertion and reason are true and reason is the correct explanation of assertion.

B

(b) If both assertion and reason are true but reason is not the correct explanation of assertion.

C

(c) If assertion is true but reason is false.

D

(d) If assertion and reason both are false.

Text Solution

Verified by Experts

The correct Answer is:
C
The beautiful colours are seen on account of interference of light reflected form the upper and the lower surfaces of the thin films. Since, condition for constructive and destructive interference depends upon the wavelength of light therefore, coloured interference fringes are observed.
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Why does a soap buuble show beautiful colours, when illuminated by white light ?

Assertion (A) : Thin films such as soap bubble or a thin layer of oil on water show beautiful colours when illuminated by white light. Reason (R ): The colours are obtained by dispersion of light

The colours seen in the reflected white light from a thin oil film are due to

Statement -1: If an exceedingly thin soap film is seen in reflected light, it may appear dark Statement -2 : Three is a phase difference of pi from the rays reflected from front and rear faces of the film.

Thin films, including soap bubbles and oil slicks, show patterns of alternating dark and bright regions resulting from interference among the reflected light waves. If two waves are in phase their crest and troughs will coincide. The interference will be constructive and the aplitude of the resultant wave will be greater than the amplitude of either constituent wave. if the two waves are out of phase, the crests of one wave will coincide with the troughs of the other wave. The interference will be destructive and the amplitude of the resultant wave will be less than that of either constituent wave. at the interface between two transparent media some light is reflected and some light is refracted. * When incident light, reaches the surface at point a, some of the light is reflected as ray R_(a) and and some is refracted following the path ab to the back of the film. *At point b some of the light is refracted out of the film and part is reflected back refracted out of the fiml as ray R_(c) . R_(a) and R_(c) are parallel. However, R_(c) has travelled the extra distance within the film of abc. if the angle of incidence is small then abc is approximately twice the film's thickness. if R_(a) and R_(c) are in phase they will undergo constructive interference and the region ac will be bright if R_(a) and R_(c) are out of phase, they will undergo destructive interference. * Refraction at an interface never changes the phase of the wave. * For reflection at the interface between two media 1 and 2, if n_(1)ltn_(2) the reflected wave will change phase by pi . if n_(1)gtn_(2) the reflected wave will not undergo a phase change. for reference n_(air)=1.00 * if the waves are in phase after refection at all interfaces, then the effects of path length in the film are Constructive interference occur when (n= refractive index) 2t=mlamda//n" "m=0,1,2,3... .. Destructive interference occurs when 2t=(m+1//2)lamda//n" "m=0,1,2,3... Q. A 600 nm light is perpendicularly incident on a soap film suspended in air. The film is 1.00 mum thick with n=1.35. Which statement most accurately describes the interference of the light reflected by the two surfaces of the film?

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Assertion (A) : The soap film in sun light is colourful Reason (R ) : Thin films produce interference of light

This question has a paragraph followed by two statements, Statement - 1 and Statement - 2. Of the given four alternatives after the statements, choose the one that describes the statements. A thin air film is formed by putting the convex surface of a plane-convex lens over a plane glass plate. With monochromatic light, this film gives an interference pattern due to light reflected from the top (convex) surface and the bottom (glass plate) surface of the film. Statement - 1: When light reflects from the air-glass plate interface, the reflected wave suffers a phase change of pi . Statement - 2 : The centre of the interference pattern is dark.

A2Z-WAVE OPTICS-Section B - Assertion Reasoning
  1. Assertion: To observe diffraction of light the size of obstacle/apertu...

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  2. Statement-I : In Young's double slit experiment interference pattern d...

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  3. Statement I: Thin films such as soap bubble or a thin layer of oit on ...

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  4. Assertion (A) : If the whole apparatus of YDSE is immersed in a liquid...

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  5. Assertion: The pattern and position of fringes always remain same even...

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  6. Statement I: In Young's double-slit experiment, the two slits are at d...

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  7. Assertion : No diffraction is produced in sound waves near a very smal...

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  8. Assertion (A) : The maximum intensity in interference pattern is four...

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  9. Assertion: In Young's double slit experiment using white light, the ce...

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  10. Assertion (A) : The unpolarised light and polarized light can be disti...

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  11. Statement I: In Young's experiment, for two coherent sources, the resu...

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  12. Assertion: When a light wave travels from a rarer to a denser medium, ...

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  13. Assertion: A narrow pulse of light is sent through a medium. The pulse...

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  14. Assertion (A) : No interfrence pattern is detected when two coherent s...

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  15. Assertion (A) : The flim which appears bright in reflected system will...

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  16. Assertion (A) : For best contrast between maxima and minima in the int...

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  17. Assertion (A) : In YDSE, the fringes become indistinct if one of the s...

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  18. Assertion (A) : The unpolarised light and polarized light can be disti...

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  19. Assertion: Nicol prism is used to produce and analyse plane polarised ...

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  20. Assertion: In everyday life to Doppler's effect is observed readily fo...

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